Neumann U67 Clone : D-U67 Tube Microphone Build Thread.

[Winetree]

Beesneez Capsule Mounting:
Do I just use the upper black cradle  from the beesneez mount
and screw it to the metal shaft on the white dome mount that came with the body?
not using the beesneez rubber iso shaft?
Don't see how I can mount the whole beesneez mount to the upper plate.
would have to drill 2 holes.

 

[wave]

More than likely yes but I need to see a pic of both mounts to say for sure

Dave

 

[Winetree]

The white mount has 2 wide spaced mounting holes.
Beesneez has 2 close spaced mounting hole in bottom brass plate.
Trouble is I can't find the right size philips head for the weird saddle screw and it's so tight the metal shaft turns.
Note; I cut the white saddle off and grabed the screw with vise grips and mounted the beesneez saddle
They used loctite on the screw.
The holes on the beesneez saddle are offset. Use one square hole and one round hole to mount capsule.

 

[imo]

i took the actual mount that came with the capsule and put it on the "white" mantle. I don't think the other one lines up with the holes

 

[dmp]

Only to find out the holes on the beesneez saddle don't line up with the holes on their capsule. The diameter's not even the same. Nothing's easy. I'm going to e-mail Beesneez.

I had to mess with it a little bit to get it to work. But I did get the screws to fit. I didn't notice a diameter issue but it did seem a little flexible.
I used the black mount that came with the capsule and mounted it on the saddle that came with the mic.

 

[imo]

I used the Beezneez mount, and put the connection to the backplane under the square hole against the capsule. That lines the holes in the capsule pretty well. Seems pretty standard to me

 

[DUDE GUY]

Anyone know why the PSU BOM includes (3) Zener diodes, 15V 5W? Thanks.

-Kevin

 

[dmp]

Anyone know why the PSU BOM includes (3) Zener diodes, 15V 5W? Thanks.

I don't know. Maybe because this is DIY and the instructions aren't perfect? 
You only need one for the psu as far as I know.
The way to develop confidence is to analyze the circuit and figure out what the components are doing.
What is the zener diode doing in the circuit?

 

[DUDE GUY]

Thanks once again, dmp. I was being paranoid that I might ruin something. I'm somewhat new to building and electronics in general and very new to PSU builds (gonna have my dad, an electrical engineer, help me with the PSU to ensure I don't hurt myself. I know this is serious stuff). From what I can tell, the Zener is used for a voltage regulator? Regulating the voltage across the tube's plate? Maybe? Again, thanks for your help, dmp. Any schooling is much appreciated.

-Kevin

 

[dmp]

Sure, no problem!
The power supply is creating two voltages for the mic, B+ (210v) and heater (-6.5v).
The U67 is complicated compared to other tube mics in that the heater supply is being set up at less than zero volts. Usually the heater would be +6.3v and 0v, while in the U67 it's -6.3v and 0v.
The zener diode is helping create that voltage below zero for the heater. The upper leg of the zener is at 0v with the lower leg at -15v. (a reverse biased zener diode always holds it's rated voltage and keeps trying to dump current). The key requirement is that the zener can only dump current until it melts down from exceeding it's power rating. In this case, 5w = 15v * max current

So the current through the zener is regulated by R2, which is conducting -15v to appx -20v at the diode bridge from the heater transformer. Current = 5v/22ohm = 227 mA.
With the power formula for the zener diode, that's 3.4 Watts (227mA*15v).
Once the -15v regulated voltage is created by the zener, the next three RC stages regulate it to a clean DC while dropping the voltage to -6.5. Note that the heater current sets the voltage drop (V=IR), so without the mic hooked up, the heater voltage will be -15v.

Be careful with the high voltages! Getting some help is a good idea.

 

[imo]

So i've sorted all of the main issues out(ground was simply a missed solder joint on the pad switch. The low pass is working, though pretty subtle. I had the 2 poles of the switch connected through one of those slip on connectors.
I have a nice Telefunken EF86. Seems like it may be quieting down, but was making that classic EF86 noise that i have come to know far too well.
Curious to hear any updated info on tube preference in the mic. I've seen some impressions through the thread, but have they changed in use?
The 'Chunger' body seems to work really well. Sure sounds like a U67 to me!
Ian

 

[Winetree]

TUBE Talk
Went on ebay and found Russian NOS '70-'80's 6j32p tubes. EF86 equivilent.
Tested, matched, etc. Low prices.
Thinking of buying some. Anybody know anything about these tubes?

 

[alexc]

Here are some measured curves and data for the 6J32P

http://www.klausmobile.narod.ru/testerfiles/6j32p.htm

I like them, but I have found quite a bit of variation in the performance of 'nos' ones.
My experience is in mic preamps, so I guess that is biased for higher current than a mic - haven't looked much at the mic circuit.
Subbing them in gave very different plate and screen currents and hence gain (no feedback connected)

I would say they are similar to ef86, but not the same - the datasheets I have used for the ef86 are fairly approximate also.

Anyway - definately worth trying but I think 1 in 3 or so gives a tube with the best performance.

Also, the microphoncs were pretty good - not much pinging or what not at reasonably high gains.

 

[Winetree]

2 builds finished. All I need are the tubes.
What brand EF86 tube did Neumann use in the orginal u67s?
Wouldn't that tube make this mic sound most like the original?

 

[gevermil]

On that note , has anyone tried the E80F / 6084 ?

 

[Jim50hertz]

2 builds finished. All I need are the tubes.
What brand EF86 tube did Neumann use in the orginal u67s?
Wouldn't that tube make this mic sound most like the original?

Great thread on this subject here.  Oliver's posts are most, ahem, "hiluminating"

 

[poctop]

The low pass is working, though pretty subtle.

Make sure you have the internal jumper IS installed as this is the default configuration,  make sure you have soldered the wire to LC jumper and not IS jumper they can get confused very easily,  the IS jumper set the curve type for the low cut operation.

Best,
Dan, 

 

[DUDE GUY]

Hello, I have a couple questions

I want to star ground and have the mic shielded, so I should use the jumper in the PSU and connect pin 3 (black wire) in the mic and at the PSU pcb, correct?

Concerning the mic cable, should I simply connect the braided shield to pin 3 on both sides of the cable and not connect the black wire inside the cable?

Any help is appreciated, thanks everyone.

-Kevin

 

[poctop]

Hello, I have a couple questions

I want to star ground and have the mic shielded, so I should use the jumper in the PSU and connect pin 3 (black wire) in the mic and at the PSU pcb, correct?

if you want to star ground, do not connect pin 3 from the mic xlr to the mic pcb ,  just leave it ,  and use the shlf jumper inside the psu

Concerning the mic cable, should I simply connect the braided shield to pin 3 on both sides of the cable and not connect the black wire inside the cable?

correct . inside the cable pin 3 becomes the cable shiled.

Any help is appreciated, thanks everyone.

-Kevin

 

[DUDE GUY]

Thanks for clarifying the star ground, Dan.

I've completed my PSU and I'm getting around 214V for the B+ and around -16V at the heater. Going by dmp's great explanation above, I'm in the right ball park, now I just need to calibrate. I tried lowering the B+ voltage using the RTRIMPLATE, but the lowest it will go is 214V. Do I need to increase the value of the pot then?

I also tried raising the voltage for the heater to -15V (mic not connected), but the RTRIM H- doesn't do anything. Maybe my wiring is wrong? Please see the attached picture. Thanks everyone.

-Kevin